With the development of network technology, users lay more and more strict requirements on the reliability of networks. Network service providers are compelled to provide secure and reliable bearer channels, and when a device or link changes, its impact on the network should be minimized.
With the rapid development of Multi Protocol Label Switch (MPLS) Virtual Private Network (VPN) technology, more and more service providers employ MPLS VPN to bear users, and in use, each Label Switch Path (LSP) is established on the basis of Label Distribution Protocol (LDP). Usually, MPLS VPN reserves a non-preferred standby link respectively for each LSP in the network, and an LDP session is pre-established on the standby link. Therefore, when a failure occurs on the primary link, the LDP may establish a new LSP on the standby link on the basis of the pre-established LDP session and then the services on the failed primary link can be recovered to be borne on the standby link. This recovering process is very short (usually several milliseconds).
However, after the original primary link has recovered to normal state, each router on the network learns the original service forward routing on the basis of Interior Gateway Protocol (IGP). Because the service forward routing of the original primary link is more preferable than that of the standby link, when the service forward routing of the original primary link which is learnt comes into effect, the LDP removes the LSP established on the standby link and attempts to establish an LSP on the original primary link. But the establishment of the LSP on the original primary link is based on an LDP session which should have been established on the original primary link, and at the moment, the LDP session has not been established on the original primary link yet, and the establishment process is relatively long (usually between ten and twenty seconds). During this process, because the LSP on the standby link has been removed and the LSP on the original primary link has not been established yet, no LSP is available to bear the service. As a result, service-bearing transmission may be seriously affected.